In a manufacturing process of a semiconductor device, a processing target object, i.e., a wafer is attracted to and held on an electrostatic chuck of a mounting table, and a plasma process such as etching process or film forming process is performed on the wafer. In general, the mounting table includes the electrostatic chuck; and a base member configured to support the electrostatic chuck. The base member is provided with a temperature control unit configured to control the temperature of the wafer. In order to perform the plasma process uniformly on an entire region of the wafer, a focus ring is provided on the base member to surround the wafer.
To perform the process uniformly on the entire region of the wafer, a temperature of the focus ring needs to be controlled with high precision. In order to control the temperature of the focus ring precisely, heat resistance between the base member of the mounting table and the focus ring needs to be reduced. For the purpose, conventionally, there has been employed a mounting table structure in which a sheet having elasticity and thermal conductivity is provided between the base member and the focus ring. An Example of such a mounting table structure is described in Japanese Patent Laid-open Publication No. 2002-016126 (Patent Document 1).
The mounting table structure in the Patent Document 1 includes a base member (mounting table), a ring-shaped member and a pressing member. The base member has a mounting surface, a ring-shaped mounting surface and a protruding part. An electrostatic chuck is provided on the mounting surface. The ring-shaped mounting surface is provided outside the mounting surface, and a focus ring is disposed on the ring-shaped mounting surface with a sheet having elasticity and thermal conductivity therebetween. The protruding part is provided outside the ring-shaped mounting surface. The ring-shaped member is fastened to the protruding part by a screw. The pressing member is fastened to the ring-shaped member by a screw with a bottom surface of the pressing member in contact with the ring-shaped member. Further, a flange of the pressing member comes into contact with a thin portion of the focus ring from above to press the focus ring against the ring-shaped mounting surface. In this mounting table structure, as the focus ring is pressed downward by the pressing member, a thickness of the sheet is reduced and the sheet is brought into firm contact with the focus ring and the base member. As a result, thermal resistance between the base member and the focus ring may be reduced.
Patent Document 1: Japanese Patent Laid-open Publication No. 2002-016126
In the mounting table structure described in Patent Document 1, a thickness decrement of the sheet is determined depending on various factors such as the thickness of the sheet, a thickness of the ring-shaped member, a thickness of the thin portion of the focus ring, a distance between the bottom surface of the pressing member and the flange in a height direction, and so forth. Therefore, it may be difficult to adjust the thickness decrement of the sheet. Further, the thickness decrement of the sheet may be varied depending on variations of the aforementioned sizes resulted from manufacturing errors. If the thickness decrement of the sheet is small, the thermal resistance between the base member and the focus ring would be increased, so that the temperature of the focus ring to which heat is transferred from plasma would also be increased. Meanwhile, if the thickness decrement of the sheet is large, a great force would be applied on the components pressing the sheet, i.e., the focus ring and the pressing member, so that these components may be damaged.
In order to adjust the thickness decrement of the sheet in the mounting table structure described in Patent Document 1, a distance between the ring-shaped member and the pressing member needs to be adjusted. For example, the pressing member needs to be fastened to the ring-shaped member by a screw while spaced apart from the ring-shaped member. In this configuration, the pressing member may be fastened to the ring-shaped member by controlling the torque of the screw precisely. Since, however, the torque of the screw changes with the lapse of time, the thickness decrement of the sheet may not be maintained constant.